Method of making stable polyvinyl acetal resins



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power-amen of e v Salim Ne. 280E125.

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\ hey end by lomtion when jeeted i'o beet. hmty has been e eerie defect end By Thie leek 0E wmeh'mvew much more use? Q V J W, i m em. My 9 invention, efl wee my novel rain we ax we the eem .o- I Ir e e. mew treetefi m eyeeoeeomee 1 521 me, flomem eifimee on by placing no my theeetflemw weld or s; end hem we e with-m amen to en m by the on owe; acid we, or (22) eluemm me me m m I We with em we eesm= in J v The fime Eee. my be the meemmm meeeee fie the men. of the el eefizellvet reme; am we eom em. In the preferred pree flee oi me fimvenmmewe or will? m mew m he 121m 1r. =m mm! .w W1 m, H? w e o m eeleoho h semen-m w the min- $110M ,j tho Wutiom r fe mmfi, Mich center, while the solution 1! vi: meiplta the and m -11 '1 it in small particles'. The B ue liquid ie-then drainedn'omthe preclm e p6; invention may he hwmemme 2e, wee, wellhememe sod! or poteesiwn acetate edoled should he more @hen equivalent to me mineral we pt. e

peefembly. W diluting the eoluiniem mm weer while the eoiltmom fls stirred mommy thereby meeeflpite the in m e Th meemieme m then washed. with water mm 2e eon moi; more '3; and, owefembixi, lees them 1% eeetie mid. The preeipfleewe end;

wed? zreem its then placed in e, keteile fin e, water we mm: m to 263% oi ethyl alcohol.

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w the mm ofmeeoll, we omen an,

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, treatment with methanol.

bilization mixture can penetrate the resin within a reasonable time. A slight rise 'in temperature also facilitates this penetration. Suitable proportions by weight are:

The resin is then centrifuged. The ceniriF-uged product will ordinarily contain residual methyl alcohol from 2 to 10% and less than 0.01% of tri-ethanol-amine, if used, and less than 0.05% of alkali salts. The resin then is dried at a temperature of 50 to 80 C., but a temperature of 100 C. or even higher may be used. While methanol appears to give the most satisfactory results it will be understood that other lower aliphatic alcohols may be advantageously employed.

The best results are obtained by employing each of the three major steps, namely, neutralization in solutioni, neutralization in suspension, and

I I find that the methanol treatment combined with neutralization in solution produces a certain definite improvement in stability, while neutralization in suspension followed by methanol treatment gives a satisfactory product only when the particle size is small, about 60 mesh. Neutralization in solution followed by neutralization in suspension produces a certain improvement in stability also while neutralization in suspension alone generally has been found unsatisfactory unless the resin is secured with a very fine particle size, about 80 mesh or finer. In general, a fine particle size is desirable to facilitate stabilization.

While the exact nature of the reactions which take place when the resin is treated in accord- I ance with my invention is somewhat uncertain, nevertheless, the great improvement in stability of the resin produced has been demonstrated by severe tests. five grams of the resin in the form of fine particles is placed in a U shaped tube of diameter and air is passed through thetube at the rate of four liters per hour while the resin is heated at a temperature of 150 0., there is no appreciable change in 'color or in solubility characteristics at the end of four hours. On the other hand, the best resins now available and which are believed to be made either by the process described in the Morrison Patent No. 2,036,092 or in French Patent No. 792,661 when given the same test darken to light brown in the-case oi formaldehyde resins, and dark brown in the case of butyraldehyde resins .before the end of four hours.

It is possible that the residual catalyst in the unstabilized resin, or foreign substances -included in the raw materials from which the resins are prepared produces unstable decomposition products. Stabilizing treatment undoubtedly removes minute residuums of the acid catalyst. It is also possible that alkyl sulfate; or halides areformed in the resin solution and the resin itself and that these are causes of insta-' For instance, I have found that if bility. The methanol may combine. with such compounds to form products which are either stable or soluble, or are volatile. It is also possible that uncombined aldehydes may be a cause 5 of instability and that they react with methanol in presence of traces of a mineral acid to produce compounds which are stable, soluble or volatile.

- Treatment in accordance with the invention effects an improvement in the stability of the resin regardless of the method used in the manufacture of the resin. However, the best results are obtained by treating resins which have been carefully prepared in accordance with the best practice known in the art. Thus, it is well known in the art that in acetalization with the higher aliphatic aldehydes, the use of too high temperature, for example, 80 C., or heating for too long a time, for example, for more than eight hours, or

the use of too large a quantity of catalyst in acetalization, such as more than 2 per cent of the weight of the total reaction mixture, tend to produce discolored resins.

be exercised to avoid all such known faulty manufacturing procedures in the preparation of resins prior to treatment in accordance with the invention if maximum stability is desired.

The present application is a division of my prior application Serial No. 280,125, filed June 20,-1939, Patent No. 2,2$s,41o, which is a continuation in-part of my application Serial No. 122,575 flied January 27, 1937.

-What is claimed is:

40 ing agent for the acid catalyst to neutralize said acid catalyst, precipitating the resin, forming an 1 aqueous suspension of the resin, subjecting the aqueous suspension of'the resin to the action-of a neutralizing agent for the acid catalyst, and

subjecting the aqueous suspension of the resin to the combined action of a saturated lower ali-' phatic monohydric alcohol and an ethanolamine.

2. In the stabilization of a polyvinyl acetal resin formed in the presence of a mineral acid catalyst,

59 the steps which comprise subjecting a solution of the resin to the action of a neutralizing agent for the acid catalyst to neutralize said acid catalyst, precipitating the'resin, forming an aqueous suspension of the resin, and subjecting the aqueous suspension of the resin to the combined action of a saturated lower aliphatic monohydric alcohol and an ethanolamine.

'3. In the stabilization of a polyvinyl acetal resin formed in the presence of a mineral acid 60 catalyst, the steps which comprise subjecting an aqueous suspension of the resin having a particle size of about 60 mesh to the action of a neutralizing agent for the acid catalyst to neutralize said acid catalyst and subjecting the aqueous suspension of the resin to'the combined action of a saturated lower aliphatic monohydric alcohol and an ethanolamine.

4. In the stabilization of a polyvinyl acetal resin .formed in the presence of a mineral acid catalyst, the steps which comprise subjecting a solution of the resin to the action of a neutralizing agent for the acid catalyst to neutralize said acid catalyst, precipitating the resin, forming an aqueous suspension of the resin, subjecting the aqueous suspension of the resin to the action 01' The use of an excess of aldehyde which will remain unreacted should 5 be avoided or the excess removed; Care should a neutralizing agent for the acid catalyst, and subjecting the aqueous suspension of the resin to the combined action of a saturated lower aliphatic monohydric alcohol and triethanolamine.

5. In the stabilization of a polyvinyl acetal resin formed in the presence of a. mineral acid catalyst, the steps which comprise subjecting a solution of the resin to the action of aneutralizing agent for the acid catalyst to neutralize said acid catalyst, precipitating theresin, forming an aqueous suspension of the resin, and subjecting the aqueous suspension of the resin to the combined action of a saturated lower aliphatic monohydric alcohol and triethanolamine.

6. Inthe stabilization of a polyvinyl acetal resin formed inthe presence of a mineral acid catalyst, the steps which comprise subjecting an aqueous suspension of the resin having a particle size of about 60 meshto the action of a neutraliz ing agent for the acid catalyst to neutralize said acid catalyst and subjecting the aqueous suspension of the resin to the combined action of a saturated lower aliphatic r'nonohydric alcohol and triethanolamine.

'7. In the stabilization of a polyvinyl acetal resin formed in the presence of a mineral acid catalyst, the. steps which comprise subjecting a solution of the resin to the action of an inorganic neutralizing agent for the acid catalyst to neutralize said catalyst, precipitating the resin, forming an aqueous suspension of the resin, and subjecting the aqueous suspension of the resin to methanol and triethanolamine.

the combined action of methanol and triethanolamine. V

8. In the stabilization of a polyvinyl acetal resin formed in the presence of a mineral acid catalyst, the steps which comprise subjecting a.- solution of the resin to the action of an inorganic neutralizing agent for the acid catalyst to neutralize said acid catalyst, precipitating the resin, forming an aqueous suspension of the resin, and subjecting the aqueous suspension of the resin to the combined action of ethanol and triethanolamina.

9. In the stabilization of a polyvinyl acetal resin formed in the presence of a mineral acid catalyst,

the steps which comprise subjecting an aqueous suspension of the resin having a particle size of about mesh to the action of an inorganic neutralizing agent for the acid catalyst to neutralize said acid catalyst, and subjecting the aqueous suspension of the resin to the combined action of 10. In the stabilization of a polyvinyl acetal resin formed in the presence of a mineral acid catalyst, the steps which comprise subjecting an aqueous suspension of the resin having a particle size of'about 60 mesh to the action of an inorganic neutralizing agent for the acid catalyst .to neutralize said acid catalyst, and subjecting the aqueous suspension of the resin to the combined action of ethanol and triethanolamine.

JOSEPH DAHLE. 

